Manufacture of paraformaldehyde



Patented Apr. 17, 1928.

UNlTED S TATEs PATENT OFFICE.

ERNST KUSS, F MANNHEIM, GERMANY,

ASSIGNOR TO I. G. FARBENINDUSTBIE TION 0F GERMANY.

MANUFACTURE OF PARAFOBMALDEHYDE.

No Drawing. Application filed June 18, 1928,

Paraformaldehyde has hitherto been prepared by concentrating dilute formaldehyde solutions or by treating such solutions wit sulfuric acid. Both processes have the greatdisadvantage ofthe products being obtained with a rathersmall ield and often being only difficultly solu le (especially when obtained by the second process referre to above) which is undesira 1e in the most cases. I have now found that paraformaldehyde can be obtained in a readily soluble form and with a good yield by preparing formaldehyde by catalytically oxidizing of methanol substantially free from water, preferably methanol of at least 98 per cent strength as completely as possible to formaldehyde, g

condensin the resulting mixture of vapors and gases y cooling preferably to about 30 C, and concentrating the resulting liquid by contact with the uncondensed gases while slightly heating it. Thereby formaldehyde solutions of about 60 per cent strength are obtained which gradually form a rather solid tallow-like mass of paraformaldehyde. As

at room temperature the formation of paraformaldehyde takes several hours for com pletion, the highly concentrated solution can be filled without difficulty in the mobile state into containers for storage or shipment an the like, and solidifies in these containers. Or the solution or paste of paraformaldehyde may be further desiccated in a vacuum evaporator whereby a dry powdery product is obtained. I

The gases not condensed by the moderate cooling of the reaction mixture contain besides nitrogen, in case the oxidation is carried out with air, and occasionally some meth l alcohol, also formaldehyde which is suitably worked up to a formaldehyde solution of 30 per cent strength.

The following example will further illustrate how my invention may be carried out in practice, but the invention is not limited to this example.

A mixture of vapors of methanol of 99.5

Serial No. 116,947, and in Germany June 24, 1925.

percent strength with so much air as to effect a complete or nearly complete oxidah tion of the alcohol to formaldehyde is continuously passed at a temperature of at least 500 C. over silver as catalyst. The resulting as mixture is rapidl cooled to about 30 and the condensed iquid while being (1 slightly heated, passed through a long pipe,

for instance a .co1l, to the discharge opening. The uncondensed gases pass the same way and concentrate the formaldehyde solution, so that it runs ofi with a strength of 60 per cent. After standing for a short time, am ple quantities of paraformaldehyde separate from this solution so that finally a tallow-like mass is formed. From each kiloram of methanol, about 800 grammes of paraformaldehyde of 60 per cent strength are obtained in this manner.

I claim:

1. The process of manufacturing paraformaldehyde which consists in catalytically oxidizing methanol substantially free from Water practically completely to formaldehyde by means of an oxygen-containing gas, cooling the reaction gases so as to condense a mixture of formaldehyde and water vapor and concentrating the resulting liquid means of the uncondensed gases and b (1 allowing the resulting concentrated solution to solidlfy.

2. The process of manufacturing araformaldehyde which consists in catalytically oxidizing methanol substantially free from Water practically completely to formaldehyde by means of an oxygen-containing gas, cooling the reaction ases so as to condense a mixture of forma dehyde and water vapor and concentratin the resulting liquid by means of the uncon ensed gases, allowing the product to solidify to a tallow-like mass and converting it into a dry powder by means of heat and a vacuum.

In testimony whereof I have hereunto set my hand.

ERNEST 'KUSS. 

